This application claims the priority of German patent document 100 28 865.0, filed Jun. 10, 2000, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a device and a process for producing a device for the catalytic generation of hydrogen from hydrocarbons, which comprises a catalytic converter. Feed and distribution channels for starting materials and discharge and collection manifolds for products are formed in the catalytic converter.
The storage of hydrogen, which is used, inter alia, as a fuel for fuel cells, is technically complex. Therefore, hydrogen is often stored in the chemically bound state, for example in the form of hydrocarbons or alcohols, and is reformed from these substances according to demand. To obtain hydrogen from hydrocarbons, a starting material mixture, which comprises hydrocarbon and water, is guided past a suitable catalytic converter with heat being supplied. If, by way of example, methanol is used as starting material, the starting materials are reacted at the catalytic converter in accordance with the following reaction equation: CH3OH+H2O→CO2+3H2.
U.S. Pat. No. 5,674,301 has disclosed a device for reforming hydrogen which comprises a porous substrate. A catalyst for the catalytic reforming of hydrogen is incorporated in the pores of the porous substrate. A hydrogen-separating thin film is provided on inner surfaces of cylindrical passages which are formed in the porous substrate.
To generate the hydrogen, hydrocarbons and steam are fed to the substrate via an end face or a lateral face of the substrate, the cylindrical passages in the substrate being sealed so that the starting materials cannot enter them. The catalytic reforming of the hydrogen takes place at the catalyst material in the pores of the porous material. The product gas, which contains carbon dioxide and hydrogen, is distributed within the porous substrate and, on account of the hydrogen-separating thin film, only the hydrogen fraction can enter the cylindrical passages. The hydrogen is then discharged via the passages, which serve as outlet channels. Non-hydrogen fractions of starting gas and product gas are discharged from the substrate via a discharge line.
In another embodiment, the catalytic converter is formed outside the porous substrate in honeycomb form. The porous substrate with the cylindrical passages is arranged directly on the flow outlet side of the honeycomb catalytic converter, the substrate itself not containing any catalyst. The end face of the porous substrate is sealed with respect to the honeycomb catalytic converter, so that product gas emerging from the catalytic converter can only flow into the passages. On entering the porous substrate, the hydrogen is separated off by means of the hydrogen-separating thin film of the passages, the passages serving as outlet channels for the product gas of the catalytic converter.
In both embodiments, the cylindrical passages in the porous substrate only form outlet channels for the hydrogen which has been separated off or the hydrogen-containing product gas of the catalytic converter. A larger inlet area for the starting-material gas is provided by the honeycomb structure of the catalytic converter.
German laid-open specification DE 197 43 673 A1, has disclosed a device for the generation of hydrogen from hydrocarbons which is composed of catalytic-converter plates. The catalytic-converter plates are produced by compressing catalyst powder to form a shaped body. Channels for supplying, distributing, discharging and collecting the starting materials and products are provided in the shaped body.
Guide channels for supplying and discharging the starting materials and products extend perpendicular to the catalytic converter plate and are arranged congruently in the individual catalytic-converter plates. In an individual catalytic-converter plate, there are only distribution channels or collection manifolds which extend parallel to the surface extent of the catalytic-converter plate in question. The device is composed of catalytic-converter plates with distribution channels for the starting materials and catalytic-converter plates with collection manifolds for the products, with these plates stacked alternately on top of one another. The distribution channels and collection manifolds of the stacked catalytic-converter plates are oriented perpendicular to one another, so that the guide channels, distribution channels and collection manifolds form a mutually orthogonal system.
Catalytic-converter plates which allow the starting materials and products to be supplied, distributed, collected and discharged in each layer can be formed by pressing and sintering further catalyst material onto catalytic-converter plates which have already been sintered, as catalytic-converter plates with complex structures.
To achieve a high yield of reaction products, it is necessary, first, to ensure a sufficiently long residence time of the starting materials on the catalyst and, second, to ensure a high flow rate through the catalytic converter. In the cited prior art, for this purpose the honeycomb catalytic converter or the complex system of channels in the catalytic converter for guiding, distributing and collecting the starting materials or products are proposed. This makes the design of the device complicated and the individual components have a complex structure, resulting in a relatively high manufacturing outlay and cost.
By contrast, the present invention is based on the object of providing a device for the catalytic generation of hydrogen which is of uncomplicated design and comprises a small number of different components which are easily structured and produced, and also a simple production process.
This object is achieved by the device and production process according to the present invention. Accordingly, feed and distribution channels for starting materials and discharge and collection manifolds for products are formed from a plurality of identically structured channels. Inlet channels are provided for supplying and distributing starting materials and outlet channels are provided for collecting and discharging products. The function as an inlet channel or an outlet channel are determined by, in each case, inversely arranged closed channel ends and open channel ends. The inlet and outlet channels extend substantially over the entire catalytic converter and are provided in an alternately intermeshing arrangement.
The use of identical channel structures for supplying, distributing, collecting and discharging starting materials or products results in a repeating structure for all the channels, so that the design of the device or of components of the device is substantially homogenized. On account of this structure, in which inlet channels for supplying and distributing and outlet channels for distributing and discharging differ only by dint of inversely closed or open ends, it is possible to achieve a highly symmetrical structure of the device according to the present invention (i.e., a design which is simple to construct and produce). By incorporating the recurring structures, a design of this type can advantageously be achieved by a small number of different components which are arranged in multiple form against one another according to the design.
The intermeshing of inlet channels and outlet channels on the one hand provides a large inlet and outlet area on the catalytic converter for the starting materials or products, and on the other hand produces a uniform spatial distribution of starting materials and products throughout the sequence of the catalytic reaction, namely the supply of the starting materials, the conversion at the catalyst, and the discharge of the products. A high flow rate combined with a sufficient residence time is ensured by the large starting-material inlet areas, reaction areas, and product-outlet areas of the catalytic converter which are created in this way.
In an advantageous configuration of the present invention, the identically structured channels are designed in the form of straight channels. Straight channels are simple to produce using numerous production processes, such as drilling, milling, pressing, and are advantageous in terms of fluid dynamics.
In an advantageous configuration of the present invention, the identically structured channels are arranged parallel to one another. In this way, it is possible to achieve a particularly uniform and symmetrical arrangement.
In an advantageous refinement of the present invention, the identically structured channels are vertical channels. Accordingly, the inlet channels extend substantially in the direction of the force of gravity. In the case of liquid metering, for example via a spray nozzle, the inlet channels may advantageously be fed with starting materials from above. The result is good distribution of the starting materials over the catalytic-converter surface. During the starting phase, it is possible, for example, for liquid methanol to collect in the inlet channel of a platinum-containing catalytic converter and to react with air, thus heating the catalytic converter. Then, when the catalytic converter has been heated, the methanol which is metered in liquid form evaporates in the inlet channel, where it is uniformly distributed.
In a further advantageous configuration of the present invention, the inlet and outlet channels taper conically in cross section from the open end towards the closed end. As a result, a larger impingement area is created in the inlet channel and/or better distribution over the surface of the inlet channel is made possible for the starting materials, in particular in the case of metering by atomization of liquids.
In a preferred embodiment of the present invention, the device is substantially composed of catalytic-converter plates which are arranged against one another and have identical surface structures. The plurality of identically structured channels and the inversely arranged open channel ends and closed channel ends are formed as the surface structure of the catalytic-converter plate which is open on one side. The inlet and outlet channels are formed between the top side and underside of adjacent catalytic-converter plates as a result of the catalytic-converter plates being joined together. The device is advantageously constructed from identical components, namely the catalytic-converter plates, which are simple to produce and have a simple structure.
In an advantageous refinement of the present invention, the surface structure of the catalytic-converter plate is designed in such a way that the plurality of identically structured channels are arranged at regular intervals and have either an odd number of inlet channels to be formed or an odd number of outlet channels to be formed. In this way, it is possible to achieve an alternating arrangement of the inlet and outlet channels in the direction of joining of the catalytic-converter plates as well, if, for example, every second catalytic-converter plate is rotated through 180° about the vertical axis of the catalytic-converter plate in the device according to the present invention. Consequently, there is no need for two types of catalytic-converter plates with an offset arrangement of inlet and outlet channels.
In a preferred embodiment of the present invention, the device comprises an upper plate and a lower plate with openings and a central section with channel sections which are open on both sides. The plurality of identically structured channels are formed by the channel sections and the open channel ends and closed channel ends are formed by the openings and closed surfaces in the upper plate and lower plate. The device according to the present invention is advantageously composed fundamentally of only three different units. The openings in the upper and lower plates may be produced by simple machining, such as drilling or stamping, or may be formed concurrently with the production, for example pressing, of the plates.
In a preferred embodiment of the present invention, the central section is composed of catalytic-converter plates with a surface structure which is arranged perpendicular to the upper plate and lower plate. The channel sections which are open on both sides are formed as surface structures of the catalytic-converter plates which are open on one side and by the catalytic-converter plates being joined together, between the upper side and underside of adjacent catalytic-converter plates. A configuration of this type allows the open channel sections to be produced by simple surface machining of the catalytic-converter plate, or alternatively they may be formed concurrently during production. The length of the channel sections which are open on both sides is predetermined by the height of the vertically arranged catalyst layers.
In a further preferred embodiment of the present invention, the central section is composed of catalytic-converter plates which are arranged parallel to the upper plate and the lower plate. The channel sections which are open on both sides being designed in the form of congruent passages in the catalytic-converter plates. In this case, it is advantageous for all three units, namely the upper plate, lower plate and catalytic-converter plates to be produced using the same process, for example drilling or milling of openings or passages. This reduces the manufacturing outlay.
In a further preferred embodiment of the present invention, the device comprises an upper plate and a lower plate with openings, side walls, and tubes with an end which is closed on one side. The tubes are arranged at the openings in the upper plate and lower plate, the plurality of identically structured channels being formed by the tubes, and the open channel ends and closed channel ends being formed by the openings in the upper plate and lower plate. The ends of the tubes which are closed on one side, and the space which is encompassed by upper plate, lower plate, and side walls is filled with catalyst material. The device is substantially composed of a small number of different components, namely plates, tubes, and side walls, which moreover are of structurally simple design. In this case, the plates, side walls, and tubes do not have to consist of catalyst material, but rather may be produced from a very wide range of materials which are selected with a view to costs and manufacturing technology. In this way, it is possible to avoid difficulties such as those which arise with the machining of catalyst material or when joining catalyst material to other materials.
In a preferred refinement of the present invention, the openings in the plate are arranged in such a way that, when the plate rotates through defined angles in the plate plane, the openings of the plate which have not been rotated are not congruent with those of the plate which have been rotated, forming offset arrangements of openings. By a corresponding arrangement of the openings, which is not symmetrical with regard to certain rotation angles, it is possible to produce upper and lower plates with one type of plate with a single arrangement of the openings on the plate. During installation, the plates are arranged rotated with respect to one another, thus producing an offset arrangement of the openings in the upper and lower plates.
In the case of rectangular or square plates, the openings on the plate are arranged in such a way that the openings are offset with respect to one another at rotation angles of 180° and 90° or 180°. In the case of circular plates, the rotation angle is not determined by the external shape of the plate, but rather by a suitable arrangement of the openings.
It will be understood that the features referred to above and those which are yet to be explained below can be used not only in the combination specified in each case but also in other combinations or on their own without departing from the scope of the present invention.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.